1. Field of the Invention:
The present invention relates to a unit that can produce hot or cold air for space heating or air conditioning.
2. Description of the Prior Art:
An electrical, oil or natural gas heater and a separate air conditioner are usually used for alternative cooling (air conditioning) or heating of interiors. In a forced air heating system, a fan or blower blows the heated air through ducts into the rooms. The evaporator or cooling unit of the air conditioner is usually located adjacent the heater unit so that the blower of the heater can blow cold air through the evaporator where it flows through the same ducting.
In the standard air conditioning thermodynamic cycle, a compressor pressurizes a working fluid (normally a fluorocarbon). The compression adds heat to the working fluid. The working fluid then flows to a condenser where the added heat is expelled to the atmosphere. Many air conditioners have the compressor and condenser mounted in a single unit outside of the house so that the heat in the condenser can be expelled to the atmosphere. The condenser is a heat exchanger and a separate blower forces outside air past the condenser where it cools the working fluid. The working fluid then travels through tubing to the evaporator, which is located adjacent to the blower of the heater in conventional home systems. The pressurized working fluid in the evaporator expands, which causes it to lose heat. The heater blower of the forced air system passes air over the cold evaporator so the air cools, and the blower forces the colder air into the house ducting. The working fluid is then pumped back into the compressor where the cycle is repeated.
Systems have also been devised to use the normally waste heat from the condenser for heating so that the system could eliminate a separate space heater. It is difficult, however, to design such a system for a portable unit. One type of portable unit is a pre-cooler unit such as that described in applicant's U.S. patent application Ser. No. 675,815, filed Nov. 28, 1984 entitled "Airplane Airconditioner." That unit is portable and designed to direct cool, air conditioned air into the cabin of an airplane while it is still on the ground. Although the main discussion in that patent application relates to cooling the cabin of an airplane parked on a hot day, there are many instances when it would be desirable to heat the inside of the cabin.
One could, in theory, use the normally wasted heat in the standard condenser for space heating purposes. There are problems in attempting to use the condenser in this way in standard air conditioning units because of natural inefficiencies in the system. The consenser is designed to maximize the exchange of heat to the outside air to increase the efficiency of air conditioning. The condenser is not necessarily properly sized for controlled heating of forced air. Also, many air conditioners use a centrifugal blower, which blows cold air into its center and force it outward. One cannot use such a blower to create the opposite air flow, which would be needed to reverse the air flow through the condenser. Making systems more complicated, makes them too large to be easily portable.